Power-assisted multidirectional jackhammer positioner

ABSTRACT

A jackhammer positioner comprising a support structure displaceably or fixedly resting on the ground, a base pivotally mounted onto the support structure, and an articulated arm pivotally connected to the base carrying a jackhammer. The articulated arm comprises two pivotally interconnected arm portions. A yoke is pivotally installed at the end of the arm opposite its connection to the base. The yoke pivotally carries a jackhammer support mechanism for carrying a jackhammer, the mechanism providing the positioner with the ability to linearly translate the jackhammer. The positioner thus comprises five pivot joints and one translation joint, and can consequently be operated to take a large number of different conformations. The operative tip of a jackhammer suspended to the positioner can thereby be easily and rapidly juxtaposed to a surface which needs to be worked.

FIELD OF THE INVENTION

The present invention relates to tool positioners, and more particularly to a jackhammer positioner with enhanced versatility and manoeuvrability features.

BACKGROUND OF THE INVENTION

A jackhammer is a very heavy tool used to break concrete structures apart for performing maintenance or repair tasks thereon. It is difficult, not to say impossible, to use jackhammers other than on the ground without mechanical assistance; for instance, it would be impossible for a construction worker to manually uplift a jackhammer and to maintain it in an uplifted position, in order to apply its operative tip on an overhanging upright wall and use the jackhammer thereon. Despite this fact, jackhammers must be sometimes used on surfaces other than ground surfaces. For example, the bottom concrete surface of bridges, outdoors concrete ceilings, upright concrete walls of a given structure, are all surfaces which may require maintenance or repair interventions with a jackhammer. In order to assist a construction worker in supporting over ground and positioning the jackhammer in a desired position, it known to use jackhammer positioners. However, existing jackhammer positioners are cumbersome, inefficient and their versatility tends to be limited.

SUMMARY OF THE INVENTION

The invention relates to a jackhammer positioner for assisting a worker in the over ground handling of a jackhammer, comprising:

-   -   a ground support member;     -   a base mounted onto said support member and moveable relative         thereto;     -   an articulated arm having first and second ends, moveably         mounted onto said base at said first end, said arm comprising a         number of displacement joints, said articulated arm further         comprising a jackhammer support member at said second end for         interconnecting said arm to the jackhammer;     -   power means for power biasing said articulated arm into a         continuously erected posture;         wherein at least three of said displacement joints are pivot         joints, and wherein one of said displacement joints is a         translation joint.

In one embodiment, said base is pivotally mounted onto said ground is support member.

In one embodiment, the range of reach of said jackhammer support member sweeps a volume represented by a virtual half sphere with said base forming approximately the center of said half sphere.

In one embodiment, said positioner further comprises control means operatively connected to and controlling said power means.

The invention also relates to an articulated support member for assisting a worker in the over ground handling of a jackhammer having a main body and a hammering head at one end of the main body thereof, said support member comprising:

-   -   an articulated arm, movable between a retracted limit first         position and an extended limit second position, said arm         defining an inner end and an outer end;     -   base means, for supporting said articulated arm spacedly over         ground;     -   first mounting means, mounting said arm inner end to said base         means for free relative movement of said articulated arm         relative to said base means;     -   power means, for power biasing said articulated arm into a         continuously erected posture;     -   a command and control unit, for securing and operating the         jackhammer in a continuously airborne fashion, said unit         defining an elongated main frame having a first end portion with         a jackhammer attachment assembly and a second end portion         opposite said first end portion with a manual command and         control template; and     -   second mounting means, interconnecting said jackhammer         attachment assembly and said arm outer end for relative movement         therebetween, for continuously maintaining the jackhammer         spacedly over ground so that the weight load of the jackhammer         be fully compensated;         wherein the range of reach of said jackhammer attachment         assembly over ground sweeps a volume represented by a virtual         half sphere with said base means forming approximately the         center of said half sphere.

In one embodiment, said second mounting means includes means for anchoring the jackhammer main body at the center of gravity thereof.

In one embodiment, said manual command and control template includes means for remote control of said power means.

In one embodiment, said articulated support member further includes translational motion means, integral to said main frame of said command and control unit for relative movement of said jackhammer attachment assembly relative to said manual command and control template.

In one embodiment, said articulated support member further includes second power means, operatively connected to said manual command and control template for selectively powering the jackhammer head in a reciprocating motion.

In one embodiment, said first mounting means includes a turntable rotatably supporting said arm inner end about an axis transverse to said turntable.

In one embodiment, said base means includes a lift platform movable vertically over ground.

In one embodiment, said first mounting means includes a turntable fixedly secured to said lift platform and rotatably supporting said arm inner end about an axis transverse to said turntable.

In one embodiment, said first mounting means includes:

-   -   an elongated rail member, fixedly mounted to said lift platform,     -   a carriage rollingly mounted to said rail member for rolling         displacement of said carriage therealong, said carriage having a         transverse frame, and     -   a turntable, fixedly secured to said carriage transverse frame         and rotatably supporting said arm inner end about an axis         transverse to said turntable;         wherein said articulated arm and associated command and control         unit are movable into a translational motion over said platform.

In one embodiment, wherein said turntable includes a central axle with low-friction PTFE coating.

The invention also relates to a jackhammer device comprising:

-   -   a jackhammer comprising a jackhammer operative tip;     -   an articulated arm supporting said jackhammer, said arm movable         between a retracted limit first position and an extended limit         second position, said arm defining an inner end and an outer         end;     -   first mounting means, interconnecting said jackhammer and said         arm outer end for relative movement therebetween;     -   base means, for supporting said articulated arm spacedly over         ground;     -   second mounting means, mounting said arm inner end to said base         means for free relative movement of said articulated arm         relative to said base means;     -   power means, for power biasing said articulated arm into a         continuously erected posture and for maintaining said jackhammer         spacedly over ground;         wherein the range of reach of said jackhammer operative tip         sweeps a volume represented by a virtual half sphere with said         base means forming approximately the center of said half sphere.

DESCRIPTION OF THE DRAWINGS

In the annexed drawings:

FIG. 1 shows a perspective view of a workman maneuvering a jackhammer installed on a jackhammer positioner according to the present invention;

FIG. 2 shows an enlarged perspective view of the support structure and one embodiment of the base of the positioner of FIG. 1;

FIG. 3 shows an enlarged cross sectional view of the support structure and the base of the positioner taken along lines III-III of FIG. 3;

FIG. 4 shows an enlarged partial perspective view of the positioner of FIG. 1;

FIG. 5 shows an enlarged perspective view of the jackhammer positioner of FIG. 1, including the jackhammer and support yoke, showing the jackhammer control mechanism;

FIG. 6 is a view similar to that of FIG. 4, but further showing in phantom lines a half-sphere suggesting jackhammer's operative tip span of accessibility;

FIG. 7 shows a perspective view of the support structure and the base of the positioner according to an alternate embodiment of the present invention, with arrow A symbolizing a force applied on the base; and

FIG. 8 shows a cross sectional view at an enlarged scale of the support structure and the base of the positioner taken along lines VIII-VIII of FIG. 7.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In FIG. 1, there is shown a workman W maneuvering a jackhammer 5 installed on a jackhammer positioner 10 according to the present invention.

Positioner 10 can be installed on a platform 1. Platform 1 is for example attached to a lifting mechanism of a utility vehicle (not shown), and can thereby be vertically raised under the action of the lifting mechanism. In one embodiment, a rail 6 is fixedly attached to platform 1, rail 6 comprising a horizontal sheet-like elongated track 6 a, and three brackets 6 b lengthwisely spaced apart along and integrally attached to track 6 a. Brackets 6 b are affixed to platform 1, and rail 6 is thus attached to platform 1, with plate 6 b being in a spaced apart and overhanging parallel relationship with platform 1.

Jackhammer positioner 10 is slidably mounted onto rail 6 of platform 1, as described hereinafter. As shown in FIG. 1-3, positioner 10 comprises a support structure 12 comprising for example two parallelely spaced-apart horizontal beams 13, and two parallelely spaced-apart tubular beams 14 extending between beams 13 and integrally attached thereto. A transverse cylindrical bushing 18 extends vertically through each beam 14 at the vicinity of their middle and is integrally attached thereto. The top edge of bushing 18 is slightly upwardly offset from the top surface of beam 14, and the internal wall of bushing 18 is covered with a bronze sleeve 21. Moreover, an upright beam 15, 15′ extends transversely, for example at right angle, from one end of each one 20 of beams 13, and is fixedly attached thereto. Two engagement wheels 16, 17 and 16′, 17′ are provided on each beam 15, 15′ respectively, and are rotatably attached thereto in a spaced-apart fashion. Upper wheels 16, 16′ of the two beams 15, 15′ form a virtual axis parallel to that extending between lower wheels 17, 17′.

Support structure 12 is slidably mounted onto rail 6. Indeed, wheels 16, 16′ slidably engage the top edge of track 6 a of rail 6, and wheels 17, 17′ slidably engage the lower edge of track 6 a of rail 6. Support structure 12 can thereby be linearly slid along track 6 a of rail 6.

Jackhammer positioner 10 further comprises a base 20, base 20 comprising a transverse axle 22 fixedly attached at the center thereof. Base 20 has a circular shape, and can be made of steel for example. Axle 22 engages bushing 18 of one beam 14 of support structure 12, and base 20 is thereby pivotally mounted thereon. In the appended figures, base 20 engages the beam 14 which is the furthest from beams 15, 15′. However, base 20 can be interchangeably mounted on either one of beams 14.

An annular washer 23, which can be coated with a friction reducing compound such as polytetrafluoroethylene (PTFE or Teflon(g), is fitted over the top edge of bushing 18 and beneath base 20. When base 20 is pivoted about its pivotal engagement with beam 14, the bottom surface of base 20 will slide with low friction onto PTFE washer 23, and axle 22 will slide against bronze sleeve 21. The pivotal movement of base 20 relative to bushing 18 is hence carried out without being excessively impeded by friction-borne forces.

As shown in FIGS. 1 and 4, a foot 20-1 is fixedly mounted onto the top surface of base 20. Positioner 10 further comprises an articulated arm 30 connected to foot 20-1, arm 30 comprising a first arm portion 32 and a second arm portion 34. Arm portions 32, 34 are tubular and are made of a material which can withstand high amounts of mechanical stress, like steel for example. Arm portion 32 is pivotally attached at one end 32A to foot 20-1, and is pivotally attached at the other end 32B to one end of arm portion 34.

A pivot actuator 24 is pivotally connected at one end 24A to foot 20-1, and is pivotally connected at the other end 24B to an intermediate section of arm portion 32. Actuator 24 can be a hydraulic or pneumatic cylinder, and is operatively connected to and controlled manually by control handles, as described hereinafter. Upon activation of actuator 24, arm 30 is pivoted about its pivotal joint with foot 20-1 between two limit positions: a first limit position, where arm portion 32 is substantially vertical and where actuator 24 is retracted, and a second limit position where arm portion 32 is pivoted downwardly into a substantially horizontal position, and where actuator 24 is extracted.

Similarly, a pivot actuator 26 is pivotally connected at one end 26A to an intermediate portion of arm portion 32, and is pivotally connected at another end 26B to an intermediate section of arm portion 34. Pivotal mount 26A is distally located compared to pivot mount 24B relative to base 20. Actuator 26 can be a hydraulic or pneumatic cylinder, and is operatively connected to and controlled by control handles, as described hereinafter. Upon activation of actuator 26, arm portion 34 is pivoted at pivotal mount 32B relative to arm portion 32 between two limit positions: a first limit position, where arm portion 34 is coaxially aligned with arm portion 32, and where actuator 26 is extracted, and a second limit position where arm portion 34 forms a large acute angle with arm portion 32, for example a 60° angle, and where actuator 26 is retracted.

Arm portion 34 integrally comprises an inner portion 38, and an attachment outer end portion 36 integrally extending from fore portion 38 in an elbowed fashion. Outer end portion 36 defines a pivot axis 37, and further comprises a cross-sectionally circular pivot pin 39 integrally axially extending from elbowed portion 36. Moreover, positioner 10 comprises a yoke 40 pivotally connected to end portion 36. As illustrated in FIG. 5, yoke 40 comprises two parallel legs 42, 42′, a crossbar 43 integrally extending between one end of ribs 42, 42′, and a pivot hole 41 recessed at the middle of crossbar 43. Pivot hole 41 is pivotally engaged by pivot pin 39 of arm portion 34, and yoke 40 is thereby pivotally attached to arm portion 36, and can therefore be pivoted about pivot axis 37. Bearings (not shown) are preferably installed at the pivot joint formed by the interconnection between pivot pin 36 and hole 41; the pivotal displacement of yoke 40 about pivot axis 37 can therefore be smoothly and frictionlessly carried out.

Yoke 40 pivotally carries a jackhammer control mechanism 50 defining a longitudinal axis 51. Mechanism 50 comprises a planar grip plate 52 defining two opposite fingers 55, 55′ laterally extending from one end thereof transversely and away from axis 51. Grip plate 52 defines a grip opening 53 recessed therethrough, whereby a workman using positioner 10 can insert his hand and hang on to displace grip plate 52. Control bars 54, 54′ integrally and co-extensively extend from both faces of plate 52, perpendicularly to planar plate 52 and parallel to longitudinal axis 51. A control handle 56, 56′ is provided at the free end of each control bar 54, 54′ respectively. Handles 56, 56′ are operatively connected to and control the activation actuators 24 and 26. Mechanism 50 further comprises a rod attachment plate 58 integrally attached to grip plate 52 perpendicularly thereto and to longitudinal axis 51. Control mechanism 50 also comprises two elongated rods 60, 60′ fixedly attached at one end thereof to attachment plate 58. Rods 60, 60′ are parallel, transversely spaced apart and symmetrically arranged relative to axis 51.

Rods 60, 60′ are slidably connected to a jackhammer attachment member 62. Attachment member 62 comprises two cylindrical hollow guides 64, 64′, each guide 64, 64′ being engaged by a corresponding registering rod 60, 60′ respectively. Guides 64, 64′ are closed at one end. The engagement between rods 60, 60′ and guides 64, 64′ is a translation joint, and rods 60, 60′ can thereby be axially slid along guides 64, 64′. Anti-egress means (not shown) should be provided within guides 64, 64′, on rod 60, 60′, or both, to prevent rods 60, 60′ from accidentally egressing from guides 64, 64′ respectively. A pivot node 70, 70′ is provided on each guide 64, 64′ respectively, and a pivot axis 71 extending between pivot nodes 70, 70′ is defined. Each leg 42, 42′ of yoke 40 is pivotally attached to a corresponding pivot node 70, 70′, and mechanism 50 can thereby be pivoted about axis 71.

Pivot nodes 70, 70′ are suitably positioned on mechanism 50 in order for the weight of jackhammer control mechanism 50 to be evenly distributed half and half on opposite sides of pivot axis 71. As a result, a workman can easily pivot mechanism 50 about axis 71, and can easily maintain it in a desired position without excessive effort.

Attachment member 62 also comprises a hollow cylindrical neck 66 coaxially carrying jackhammer 5. The main body of jackhammer 5 is partially engaged by and secured to neck 66, and the elongated operative free end tip 7 of jackhammer 5 is arranged coaxially with longitudinal axis 51, opposite handles 56, 56′.

Mechanism 50 is further provided with two actuators 68, 68′, which are operatively connected to and controlled by handles 56. Actuators 68, 68′ are preferably hydraulic cylinders, and therefore possess a chamber end and a piston rod end. The chamber end of each actuator 68, 68′ is firmly connected to a finger 55, 55′ respectively of grip plate 52, and the piston rod end is connected to a corresponding pivot node 70, 70′. Upon activation of actuators 68, 68′, guides 64, 64′ of jackhammer attachment member 62 are slid along rods 60, 60′. Jackhammer 5 being affixed to jackhammer attachment member 62, as actuators 68, 68′ are activated, jackhammer 5 is translated away or towards rod attachment plate 58 between two limit positions: a first limit position where rods 60, 60′ are brought to their outward most extended limit position guides 64, 64′, and a second limit position where rods 60, 60′ are brought to their inward most retracted condition on the closed end portion of guides 64, 64′.

Since pivot nodes 70, 70′ of attachment member 62 link mechanism 50 to the rest of positioner 10, the displacement of attachment member 62 affects the conformation of positioner 10. Indeed, as actuators 68, 68′ are activated for translational motion of attachment member 62, base 20 and arm portions 32, 34 can be concurrently pivoted to follow the displacement of attachment member 62.

To use jackhammer positioner 10, platform 1 must be positioned at the vicinity of a structure which needs to be worked. Thereafter, the positioner 10 must be manually operated by workman W to position jackhammer 5, in order to juxtapose the operative tip 7 of jackhammer 5 in close proximity to the structure which needs to be worked.

Base 20, as well as arm 30 installed on base 20, can be manually pivoted for a full turn (360°) about vertical axle 22, to sweep a circular horizontal area overhanging horizontal platform 1.

Moreover, handles 56, 56′ can be manipulated by worker W to effortlessly control hydraulic actuators 24, 26; upon activation of actuators 24, 26, arm portions 32, 34 can be pivotally articulated about their shoulder joint 24A and elbow joint 32B, to retract or extend arm 30 within a vertical plane.

Furthermore, workman W can pivot yoke 40 about pivot axis 37, to rotate for up to a full turn the jackhammer 5 about the lengthwise axis of the latter. Workman W can also grip plate 52 by grip opening 53 and manually pivot mechanism 50 about pivot axis 71.

Also, by appropriately maneuvering handles 56, 56′ and activating actuators 68, jackhammer 5 can be moved in translation axially along longitudinal axis 51 between its first extended position and second retracted limit positions, as guides 64, 64′ of attachment member 62 are slidably driven back and forth along rods 60, 60′.

Finally, support structure 12 can be slid along rail 6 of platform 1, and the whole positioner 10 can thereby be linearly displaced over platform 1.

Jackhammer 5 is then conventionally activated, and the work can take place. An electric line 80 interconnects handles 56, 56′ to jackhammer 5, and a pneumatic line 82 interconnects jackhammer 5 to a pressurized air source. When the workman manipulates handles 56, 56′ to selectively activate jackhammer 5, handles 56, 56′ will send an electric activation signal to jackhammer 5. As a result thereof, pressurized air is injected into jackhammer 5 through the instrumentality of pneumatic line 82 to enable repeated back and forth hammering action of jackhammer tip 7 against the surface to be treated.

By providing a positioner with such relative displacement features, positioning the jackhammer in a desired position is effortless and easily accomplished. The positioner is versatile and can be operated to take numerous different conformations. Indeed, as illustrated in FIG. 6, the positioner can be manipulated to position operative tip 7 of jackhammer 5 at any point located within at least the volume of a half-sphere 100. The center of half-sphere 100 corresponds to pivotal base 20, and its radius corresponds approximately to the maximum distance which can separate the free extremity of operative tip 7 of jackhammer 5 and base 20 (when arm is fully extended pivotally about hinge 32B).

Jackhammer positioner 10, as described herein, possesses additional advantageous features. In the prior art, when a workman W handles a jackhammer directly, the operative tip 7 thereof forcefully and repeatedly pounds onto a concrete structure in reciprocating fashion, and the hands of the workman W are consequently jarred. On the contrary, in positioner 10 of the present invention, jackhammer 5 is not directly in contact with the workman; jackhammer 5 is attached to support member 62, which can recoil and slide along rods 60 every time operative tip 7 pounds on concrete. 20 The reciprocating motion of the jackhammer 5 is thus not transmitted to the workman using jackhammer 5 when it is installed on positioner 10, and the workman's hands are hence less, or even not at all jarred.

Alternative embodiments of the invention will now be described. As illustrated in FIGS. 7-8, there is shown a beam 114 of an alternate support structure 112, provided with a transverse cylindrical channel 118 extending therethrough. A discoid pivot plate 119 having a pivot hole 11 9a at its center is fixedly attached to the internal walls of channel 118. A base 120, comprising a transverse axle 122 fixedly extending from its center, is pivotally mounted on beam 114. Indeed, axle 122 pivotally engages pivot hole 119a, and base 120 abuts on a PTFE washer 123 fitted between the top edge of channel 118 and the bottom surface of base 120.

Channel 118 has a diameter which is equal or slightly inferior to that of base 120.

If base 120 is subjected to an off-centred force A, base 120 will tend to tilt laterally. Since channel 118 is slightly smaller in diameter than base 120, the top peripheral edge of channel 118 will peripherally support base 120. Such a tilting motion, which would be likely to provoke bending and permanent damage of axle 122, is hence accounted for by inherent tilt compensation.

In another alternate embodiment (not illustrated in the appended drawings), support structure 12 is not slidable about a rail. Rather, support structure 12 is fixedly anchored on platform 1, and therefore can not be linearly displaced.

Certain modifications and improvements will occur to those skilled in the art upon a reading of the foregoing description. It should be understood that all such modifications and improvements have been omitted herein for the sake of conciseness and readability but are properly within the scope of the following claims. 

1. A jackhammer positioner for assisting a worker in the over ground handling of a jackhammer, comprising: a ground support member; a base mounted onto said support member and moveable relative thereto; an articulated arm having first and second ends, moveably mounted onto said base at said first end, said arm comprising a number of displacement joints, said articulated arm further comprising a jackhammer support member at said second end for interconnecting said arm to the jackhammer; power means for power biasing said articulated arm into a continuously erected posture; wherein at least three of said displacement joints are pivot joints, and wherein one of said displacement joints is a translation joint.
 2. A jackhammer positioner as in claim 1, wherein said base is pivotally mounted onto said ground support member.
 3. A jackhammer positioner as in claim 2, wherein the range of reach of said jackhammer support member sweeps a volume represented by a virtual half sphere with said base forming approximately the center of said half sphere.
 4. A jackhammer positioner as in claim 1, further comprising control means operatively connected to and controlling said power means.
 5. An articulated support member for assisting a worker in the over ground handling of a jackhammer having a main body and a hammering head at one end of the main body thereof, said support member comprising: an articulated arm, movable between a retracted limit first position and an extended limit second position, said arm defining an inner end and an outer end; base means, for supporting said articulated arm spacedly over ground; first mounting means, mounting said arm inner end to said base means for free relative movement of said articulated arm relative to said base means; power means, for power biasing said articulated arm into a continuously erected posture; a command and control unit, for securing and operating the jackhammer in a continuously airborne fashion, said unit defining an elongated main frame having a first end portion with a jackhammer attachment assembly and a second end portion opposite said first end portion with a manual command and control template; and second mounting means, interconnecting said jackhammer attachment assembly and said arm outer end for relative movement therebetween, for continuously maintaining the jackhammer spacedly over ground so that the weight load of the jackhammer be fully compensated; wherein the range of reach of said jackhammer attachment assembly over ground sweeps a volume represented by a virtual half sphere with said base means forming approximately the center of said half sphere.
 6. A support member as in claim 5, wherein said second mounting means includes means for anchoring the jackhammer main body at the center of gravity thereof.
 7. A support member as in claim 5, wherein said manual command and control template includes means for remote control of said power means.
 8. A support member as in claim 5, further including translational motion means, integral to said main frame of said command and control unit for relative movement of said jackhammer attachment assembly relative to said manual command and control template.
 9. A support member as in claim 5, further including second power means, operatively connected to said manual command and control template for selectively powering the jackhammer head in a reciprocating motion.
 10. A support member as in claim 5, wherein said first mounting means includes a turntable rotatably supporting said arm inner end about an axis transverse to said turntable.
 11. A support member as in claim 5, wherein said base means includes a lift platform movable vertically over ground.
 12. A support member as in claim 11, wherein said first mounting means includes a turntable fixedly secured to said lift platform and rotatably supporting said arm inner end about an axis transverse to said turntable.
 13. A support member as in claim 11, wherein said first mounting means includes: an elongated rail member, fixedly mounted to said lift platform, a carriage rollingly mounted to said rail member for rolling displacement of said carriage therealong, said carriage having a transverse frame, and a turntable, fixedly secured to said carriage transverse frame and rotatably supporting said arm inner end about an axis transverse to said turntable; wherein said articulated arm and associated command and control unit are movable into a translational motion over said platform.
 14. A support member as in claim 12, wherein said turntable includes a central axle with low-friction PTFE coating.
 15. A jackhammer device comprising: a jackhammer comprising a jackhammer operative tip; an articulated arm supporting said jackhammer, said arm movable between a retracted limit first position and an extended limit second position, said arm defining an inner end and an outer end; first mounting means, interconnecting said jackhammer and said arm outer end for relative movement therebetween; base means, for supporting said articulated arm spacedly over ground; second mounting means, mounting said arm inner end to said base means for free relative movement of said articulated arm relative to said base means; power means, for power biasing said articulated arm into a continuously erected posture and for maintaining said jackhammer spacedly over ground; wherein the range of reach of said jackhammer operative tip sweeps a volume represented by a virtual half sphere with said base means forming approximately the center of said half sphere. 